A thyristor may be simplistically viewed as a four-layer semi-conducting device, with each layer comprising an alternate N- or P-type material, for example NPNP. In some cases, the thyristor may be represented schematically or modeled as a pair of collector-to-base and base-to-collector tightly coupled bipolar transistors. The opposite ends of the device may be labeled anode-emitter and cathode-emitter while regions therebetween may be referenced as n-base and p-base regions, respectively. In a particular device, a control electrode may be operable to influence one of the intermediate base regions during operation of the thyristor.
In a thin capacitively-coupled thyristor device, one of the base regions of the thyristor may be capacitively coupled to an electrode. In some applications, the electrode capacitively coupled to the base may be controlled to assist switching of the thyristor; e.g., switching from a conducting state to a blocking state. Further, the base region of the thyristor may be made thin enough so that the capacitor electrode, when activated, can fully deplete the base region of minority carriers to assist transition of the thyristor into its blocking state.
In some cases, the thyristors may be described as a type of negative differential resistance (“NDR”) device, which may be used in forming a thyristor-based memory device. Some propose that the use of these types of memory could potentially provide the speed of conventional static random access memory (“SRAM”) while at the same time the density of dynamic random access memory (“DRAM”). Additionally, these devices might also be capable of fabrication using available process equipment of the complementary metal-oxide semiconductor (“CMOS”) fabrication industry.
In some applications, thyristors and/or thyristor-based memory arrays might also be embedded or integrated together with other semiconductor logic devices. For example, an integrated logic device may use a memory cell to temporarily hold an input value before the input value is to be communicated to further logic circuitry for calculations. Thus, a logic device may use a thyristor-based memory as a component for temporary storage before performing a system calculation via other components of the device.
One consideration in any type of semiconductor device may be its switching speed—the time needed for a device to transition from storing or outputting one value to storing or outputting another value. Another consideration may be the propagation speed of these devices. A variety of factors may influence the propagation and switching speed of a semiconductor device. Naming a few, such factors may include carrier mobility, device resistance, device capacitance, and the like.